DIRECT STELLAR RADIATION PRESSURE AT THE DUST SUBLIMATION FRONT IN MASSIVE STAR FORMATION: EFFECTS OF A DUST-FREE DISK

In massive star formation (greater than or similar to 40 M-circle dot) by core accretion, the direct stellar radiation pressure acting on the dust particles exceeds the gravitational force and interferes with mass accretion at the dust sublimation front, the first absorption site. Ram pressure generated by high accretion rates of 10(-3) M-circle dot yr(-1) is thought to be required to overcome the direct stellar radiation pressure. We investigate the direct stellar irradiation on the dust sublimation front, including the inner accretion disk structure. We show that the ram pressure of the accretion disk is lower than the stellar radiation pressure at the dust sublimation front. Thus, another mechanism must overcome the direct stellar radiation pressure. We suggest that the inner hot dust-free region is optically thick, shielding the dust sublimation front from direct stellar irradiation. Thus, accretion would not halt at the dust sublimation front, even at lower accretion rates.